A wide variety of techniques for positioning a cursor on a computer display are available and well known in the computer industry. Conventional cursor control devices include, for example, mice, track balls, touch screens, joy sticks, and light pens. Cursor control devices are also commonly referred to as pointing devices, as they allow a user to select (or "point to") a specific location on a computer screen.
Conventional cursor control devices generally suffer from one or more deficiencies. For example, many cursor control devices, such as a typical mouse, require the user to move his or her hand across large areas to operate efficiently and permit movement of the cursor throughout the display area. Often, a user's workspace is limited, and the user must repeatedly lift, move and set down the mouse in order to move the cursor across the screen. In such situations, use of a mouse is inconvenient and frustrating. It can also lead to physical fatigue and repetitive stress injuries.
In order to overcome many of the disadvantages of conventional cursor control devices, improved cursor positioning devices have been developed, such as the patented FELIX.TM. devices produced by Altra Corporation. Devices of this type are disclosed in U.S. Pat. Nos. 4,782,327, issued on Nov. 1, 1988 and 4,935,728, issued on Jun. 19, 1990; these patents are hereby incorporated by reference in their entirety (and referred to herein as the "Kley Patents"). Devices such as Altra's FELIX.TM. device permit comfortable movement of a cursor using finger, not wrist or arm, movements. These devices allow for great precision of movement and, in many cases, a cursor can be moved across an entire computer screen by moving a finger less than one square inch.
Recently, attempts have been made to improve further the effectiveness of devices such as those described in the Kley Patents. For example, Taiwan U.M. Application No. 84205829 (Publication No. 283506) (hereinafter referred to as the "Taiwan Application"), describes a mechanical optical absolute coordinate cursor control device claimed to provide advantages over the prior art. A rough translation of the specifications and claims of the Taiwan Application, along with relevant drawings, is attached as Appendix A and fully incorporated herein by reference.
It will be apparent to those skilled in the art that the Taiwan Application describes mainly well-known technology, contains numerous flaws, and fails to provide technical support for advantages claimed in the application. For example, as part of the described mechanical optical control device, the Taiwan Application describes the use of optical grating plates to detect position changes, a technique which is well known in the art. In the Taiwan Application, however, the grating plates are configured in upper and lower rows with a 90 degree phase displacement between the rows. The Taiwan Application erroneously asserts that use of the grating plates as described in the Taiwan application permits the unique detection of the minimum and maximum values at the two end boundaries. In fact, this claim is false, and the Taiwan Application fails to provide a disclosure that would enable the relevant claims or advantages. Accordingly, there is a need for inventive improvements to the well known technology described in the Taiwan Application to permit the technology to function properly.
In addition to the problems of the device described in the Taiwan Application, prior art pointing devices in general also exhibit many other deficiencies. For example, most pointing devices employ switches, such as the switches operated (i.e., opened or closed) when a user "clicks on" a particular point on the display to select that point for further operations. Detection of state changes in a switch by digital means, however, is often unreliable due to detection of false switching cycles. This problem, for example, can lead to difficulties in distinguishing "double-clicks" from "single clicks." The difficulty is that "on-off-on" or "off-on-off" activity may be erroneously detected, when in reality the switch is simply bouncing as a result of changing state once, from "on" to "off" or from "off" to "on." All switches will, to some extent, exhibit such behavior (called switch bounce).
Accordingly, there is a need for an improved cursor control device that eliminates disadvantages associated with prior art devices generally and with the device described in the Taiwan application in particular.